As the grain size of magnetic recording media is decreased in order to increase the a real density, a threshold known as the superparamagnetic limit is reached for a given material and temperature. The superparamagnetic limit is a physical constraint, beyond which stable data storage is no longer feasible.
Thermal stability of magnetic recording systems can be improved by employing a recording medium formed of a material with a very high magnetic anisotropy Ku. The energy barrier for a uniaxial magnetic grain to switch between two stabilized states is proportional to the product of the magnetic anisotropy Ku of the magnetic material and the volume (V) of the magnetic grains. In order to provide adequate data storage, the product KuV should be as large as 60 kBT, where kB is the Boltzman constant and T is the absolute temperature, in order to provide 10 years of thermally stable data storage. Although it is desirable to use magnetic materials with high Ku, very few of such hard magnetic materials exist. Furthermore, with currently available magnetic materials, recording heads are not able to provide a sufficient magnetic writing field to write on such materials.
Heat assisted magnetic recording (HAMR) refers to the concept of locally heating a magnetic recording medium to reduce the coercivity of the recording medium so that the applied magnetic writing field can more easily direct the magnetization of the recording medium during the temporary magnetic softening of the recording medium caused by the heat source. Heat assisted magnetic recording (HAMR) systems for writing information on a magnetic medium employ a combination of a magnetic write field gradient and a thermal gradient, which is proposed to extend magnetic recording beyond 1 Terabit per in2. HAMR allows for the use of small grain media, which is desirable for recording at increased areal densities, with a larger magnetic anisotropy at room temperature assuring sufficient thermal stability.
Several key requirements of the HAMR media include high anisotropy, moderate Curie temperature and good microstructure with thermally well-isolated grains. Among the media candidates, it remains a challenge to satisfy all the three requirements simultaneously.
A need therefore exists for recording films that can effectively be used for heat assisted magnetic recording.